1. Field of the Invention
The present invention relates to a semiconductor device and a method of manufacturing the same, and more particularly to a semiconductor device having a gate electrode formed to fill a trench and a method of manufacturing the same.
2. Description of the Background Art
There are semiconductor devices including a main electrode for supplying a current to be switched, i.e., a main current, to a semiconductor layer, and a gate electrode for applying an electric field to the semiconductor layer, and performing switching by controlling a channel of the semiconductor layer with the electric field generated by the gate electrode. A MOS (Metal Oxide Semiconductor) transistor or an IGBT (Insulated Gate Bipolar Transistor) are representative examples of such semiconductor devices. Particularly in power control applications, a structure in which a number of cells each capable of performing switching operation are connected in parallel is common.
Some of such semiconductor devices including a number of cells have a function of monitoring a main current in order to check whether it is excessive or not. According to Japanese Patent No. 3361874, for example, a semiconductor device includes a number of main IGBT cells for switching a main current, as well as sense IGBT cells for switching a smaller sense current corresponding to the main current, and monitors the main current in order to check whether it is excessive or not by detecting the sense current.
It is known that a surge may occur in the sense current during turn-on. The reason why the surge occurs may be because sense IGBT cells turn on earlier than main IGBT cells due to a slight structural difference or manufacturing variations between the main IGBT cells and the sense IGBT cells, and a current that flows as a result thereof flows through the sense IGBT cells considerably smaller in number than the main IGBT cells. When a surge occurs in the sense current, a main current is erroneously recognized as being excessive, which results in unnecessary operation for protecting the semiconductor device against overcurrent.
In order to delay turn-on of the sense IGBT cells, therefore, according to the technique in Japanese Patent No. 3361874 described above, a voltage threshold value of the sense IGBT cells is set higher than a voltage threshold value of the main IGBT cells.